1. Using UNetbootin (for Windows and Linux)

UNetbootin allows you to create bootable Live USB drives for a variety of Linux distributions from Windows or Linux, without requiring you to burn a CD. You can either let it download one of the many distributions supported out-of-the-box for you, or supply your own Linux .iso file if you've already downloaded one or your preferred distribution isn't on the list.

Installation & Screenshots

If using Windows, run the file, select a distribution, floppy/hard disk image, or kernel/initrd to load, select a target drive (USB Drive or Hard Disk), then reboot once done.

If using Linux, make the file executable (using either the command chmod +x ./unetbootin-linux, or going to Properties->Permissions and checking "Execute"), then start the application, you will be prompted for your password to grant the application administrative rights, then the main dialog will appear, where you select a distribution and install target (USB Drive or Hard Disk), then reboot when prompted.

After rebooting, if you created a Live USB drive by selecting "USB Drive" as your install target, press the appropriate button (usually F1, F2, F12, ESC, or backspace) while your computer is starting up to get to your BIOS boot menu and select USB drive as the startup target; otherwise if there's no boot selection option, go to the BIOS setup menu and change the startup order to boot USB by default. Otherwise, if you did a "frugal install" by selecting "Hard Disk" as your install target, select the UNetbootin entry from the Windows Boot Menu as the system boots up.

To create a Live USB using UNetbootin, download an ISO file, select it under UNetbootin's "diskimage" option, and specify your target USB disk under "Drive:". After pressing OK, wait as the ISO is extracted to your USB drive; once done, you will have a bootable Linux Mint Live USB drive.

Requirements

1 GB or larger USB drive, formatted as Fat32 (most USB drives come formatted as FAT32 by default, but if you need to format it, on Windows, go to My Computer->right click your USB drive->format, or on Linux, use GParted or another partition manager)

Supported operating systems: Windows 2000 and above OR a modern Linux distribution

Update: Ubuntu now includes "Startup disk creator". You can access it via System > Administration > Startup Disk Creator and it's a very easy to use tool. Simply enter your memory stick into the USB drive, then open Startup Disk Creator and select "Format" (the USB stick needs to be formatted first), then select the ISO image you want to write on the USB memory stick and click "Make startup disk". That's it.

4. Using Diskutil (Mac OS X only)

Download the desired .img file

Open a Terminal (under Utilities)

Run diskutil list to get the current list of devices

Insert your flash media

Run diskutil list again and determine the device node assigned to your flash media (e.g. /dev/disk2)

Run diskutil unmountDisk /dev/diskN

Execute sudo dd if=/path/to/downloaded.img of=/dev/diskNbs=1m

Run diskutil eject /dev/diskN and remove your flash media when the command completes